The supplies of liquid blood are currently limited by storage systems used in conventional blood storage practice. Using current systems, stored blood expires after a period of about 42 days of refrigerated storage at a temperature above freezing (i.e., 4° C.) as packed blood cell preparations. Expired blood cannot be used and must be discarded because it will harm the ultimate recipient. One of the primary reasons for blood spoilage is its continued metabolic activity after it is stored. For example, in 2007, more than 45 million units of red blood cells (RBCs) were collected and stored globally (15.6 million in the US). During refrigerated storage, RBCs become progressively damaged by storage lesions. When transfused within the current 6-week limit, stored RBCs have lower quality (fraction of RBC removed; compromised O2 delivery capacity) as well as potential toxicity, often manifested as side effects of transfusion therapy. These storage lesions are observed as altered biochemical and physical parameters associated with stored cells. Examples of these include in vitro measured parameters such as reduced metabolite levels (ATP and 2,3-DPG), reduced surface area, echinocytosis, phosphatidylserine exposure, and reduced deformability.
Stored blood undergoes steady deterioration which is partly caused by hemolysis, hemoglobin degradation and reduced adenosine triphosphate (ATP) concentration that occur during the storage period. These reasons and others limit the amount of readily available high quality blood needed for transfusions.
As discussed above, when RBCs are stored under refrigeration at temperatures above freezing (e.g., 1-6° C., standard storage conditions) in a blood storage bag, away from mechanical stress and the constantly cycling environment of the circulation, the senescence process is partially suspended. However, with the lack of constant nutrient replenishment and waste removal under refrigerated storage, RBCs are gradually damaged, resulting in compromised physiological functions. By way of example, the following problems occur during extended storage:                When RBCs are stored for an extended period, storage lesions accumulate and deteriorate RBCs and cause up to 1% of RBCs to be hemolyzed during storage and up to 25% to be removed shortly after transfusion.        Non-viable RBCs cause iron overload in chronically transfused patients.        Transfusion does not always achieve the intended outcome of increased tissue perfusion.        Hemoglobin in RBCs do not release oxygen efficiently at tissues due to loss of 2,3-DPG.        RBCs are not able to enter and perfuse capillary beds due to loss of deformability.        
Transfusing RBCs stored for longer periods may result in higher morbidity and longer hospital stays compared to transfusing “fresher” red cells. Higher morbidity and longer hospital stays result with RBCs that are stored longer than 6 weeks, in comparison to fresher red cells. For example, negative clinical outcomes in cardiac surgery occur when using ‘older’ blood; multiple organ failure in surgical patients reflecting the age of transfused red cells; correlation between older units and increased mortality in severe sepsis; failure to improve O2 utilization attributed to decreased 2,3-DPG and decreased cardiac index associated with increased blood viscosity
This evidence suggests that the ineffectiveness and negative consequences of transfusion is attributable at least in part to the compromising effects of extended storage of RBCs. In addition to immediate removal by the recipient of certain RBCs, consequences of RBC storage lesions include: (i) Depletion of ATP (loss of RBC's ability to dilate the pre-capillary arteriole); (ii) Depletion of 2,3-DPG; (iii) Accumulation of oxidative damage caused by reactive oxygen species (ROS) formed by the reaction of denatured hemoglobin with O2; and (iv) Decreased RBC deformability and increased RBC viscosity-caused in part by oxidative damage to membrane and cytoskeleton. Less deformable RBCs are excluded from capillary channels resulting in low capillary occupancy and reduced tissue perfusion. Massive transfusion of un-deformable cells may also contribute to multiple organ failure by blocking the organs' capillary beds. After transfusion, 2,3-DPG is synthesized relatively quickly in vivo to ˜50% of the normal level in as little as 7 hours and to ˜95% of the normal level in 2-3 days . However, since 2,3-DPG-depleted cells do not recover their levels immediately, O2-carrying capacity is compromised to the detriment of critically ill patients requiring immediate O2 delivery and tissue perfusion. There are numerous reports that emphasize the importance of RBCs with high oxygen carrying capacity in such clinical situations.
Storage of frozen blood is known in the art but such frozen blood has limitations. For a number of years, frozen blood has been used by blood banks and the military for certain high-demand and rare types of blood. However, frozen blood is difficult to handle. It must be thawed which makes it impractical for emergency situations. Once blood is thawed, it must be used within 48 hours. U.S. Pat. No. 6,413,713 to Serebrennikov is directed to a method of storing blood at temperatures below 0° C.
U.S. Pat. No. 4,769,318 to Hamasaki et al. and U.S. Pat. No. 4,880,786 to Sasakawa et al. are directed to additive solutions for blood preservation and activation. U.S. Pat. No. 5,624,794 to Bitensky et al., U.S. Pat. No. 6,162,396 to Bitensky et al., and U.S. Pat. No. 5,476,764 are directed to the storage of red blood cells under oxygen-depleted conditions. U.S. Pat. No. 5,789,151 to Bitensky et al. is directed to blood storage additive solutions.
Additive solutions for blood preservation and activation are known in the art. For example, Rejuvesol (available from enCyte Corp., Braintree, Mass.) is added to blood after cold storage (i.e., 4° C.) just prior to transfusion or prior to freezing (i.e., at −80° C. with glycerol) for extended storage. U.S. Pat. No. 6,447,987 to Hess et al. is directed to additive solutions for the refrigerated storage of human red blood cells.
The effects of elevation and preservation of ATP levels in blood storage situations has been studied. For example, in “Studies In Red Blood Cell Preservation-7. In Vivo and in Vitro Studies With A Modified Phosphate-Ammonium Additive Solution,” by Greenwalt et al., Vox Sang 65, 87-94 (1993), the authors determined that the experimental additive solution (EAS-2) containing in mM: 20 NH4Cl, 30 Na2HPO4, 2 adenine, 110 dextrose, 55 mannitol, pH 7.15, is useful in extending the storage shelf-life of human RBCs from the current standard of 5-6 weeks to an improved standard of 8-9 weeks. Packed RBCs are suitable for transfusion following the removal of the supernatant with a single washing step. Greenwalt et al. also conclude that factors other than ATP concentration appear to play an increasingly important role in determining RBC viability after 50 days of storage. They cite the results of L. Wood and E. Beutler in “The Viability Of Human Blood Stored In Phosphate Adenine Media,” Transfusion 7, 401-408 (1967), find in their own experiments that the relationship between ATP concentration and 24-hour RBC survival measurements appear to become less clear after about 8 weeks of storage. E. Beutler and C. West restate that the relationship between red cell ATP concentration and viability is a weak one after prolonged periods of storage in “Storage Of Red Cell Concentrates In CPD-A2 For 42 and 49 Days,” J. Lab. Clin. Med. 102, 53-62 (1983).
In “Effects Of Oxygen On Red Cells During Liquid Storage at +4° C.,” by Hogman et al., Vox Sang 51, 27-34 (1986), the authors discuss that red cell content of ATP is slightly better maintained in anaerobic chamber than at ambient air storage after 2-3 weeks. Venous blood was refrigerated and deprived of additional oxygen during storage, by placing the oxygen-permeable storage bags in a nitrogen environment and thereby gradually reducing the level of oxygen saturation. The reduction in oxygen concentration occurs slowly during storage at 4° C., and is far from complete, starting at about 60% and reaching about 30% hemoglobin saturation at 5 weeks. No conclusion could be drawn concerning the effects of this procedure on the overall quality of stored cells. These authors did not address or significantly reduce the oxygen-dependent damage to hemoglobin and the oxygen-mediated damage caused by hemoglobin breakdown products.
Many patents have addressed different aspects of blood storage. One such patent is U.S. Pat. No. 4,837,047 to Sato et al. which relates to a container for storing blood for a long period of time to keep the quality of the blood in good condition. Sato et al. is directed at improving the storage life of the stored blood by maintaining a partial pressure of carbon dioxide gas in the blood at a low level. Such partial pressure is apparently obtained through normalization with the outside atmosphere. The container is made of a synthetic resin film which has a high permeability to carbon dioxide gas for the purpose of making it possible for the carbon dioxide gas to easily diffuse from the blood to outside. However, the problems caused by the interaction of the oxygen and hemoglobin in the blood are not addressed.
Another patent, U.S. Pat. No. 5,529,821 to Ishikawa et al. relates to a container and a method for the storage of blood to prevent adhesion of the blood to the container. Blood is stored in containers composed of a sheet material having a plurality of layers where a first sheet which contacts the blood substantially prevents the activation and adhesion of blood platelets to the layer. Again, however, the problems caused by the interaction of the oxygen and hemoglobin in the blood are not addressed.
In light of current technology, there is a need to improve the quality of red blood cells that are to be stored and to extend the storage life of such red blood cells in advance of transfusion to minimize morbidity associated with transfusions.